Contents

Design

Seiko is a teenage girl with below average height and build. She has light brown eyes and long brown hair (colored orange in the manga adaptation) that she styles into two curls on both sides of her head, just beneath her ears. She also wears a blue barrette on the left side of her head. Seiko has a natural kitty mouth/smile, which is especially noticeable when she's being devious and/or perverted.

Like all other female students at Kisaragi Academy, she wears a tan-colored sailor outfit with a blue collar and lighter blue cuffs. Her uniform also consists of a yellow bow held by a blue brooch to the top and a blue pleated skirt. Her student ID is pinned to the bottom of her top. Seiko also wears black mid-calf socks and blue uwabaki slippers.

Personality

Seiko is an extremely cheerful and energetic girl who enjoys playing around with her friends. She often comes across as immature and crass and makes over-the-top outbursts that surprise everyone around her, but her friends are able to put up with it. She generally tries to maintain this personality even while trapped inside Heavenly Host, though the grim reality of their situation nearly causes her to suffer from an emotional breakdown several times.

She is not without a responsible side, however, which she developed after her mother disappeared two years ago in order to support her father and care for her three younger siblings. She easily becomes upset whenever anyone takes her feelings towards her mother's disappearance lightly.

Plot

Corpse Party

CHAPTER 1

Seiko stays after school with her class during Kisaragi Academy's cultural festival to listen to Ayumi Shinozaki's ghost stories about Heavenly Host Elementary School. As they prepare to leave, Ayumi decides to perform the Sachiko Ever After charm with her classmates to comfort Mayu Suzumoto over her upcoming school transfer. Shortly after they perform the ceremony, an earthquake occurs and opens a gaping hole in the floor that Seiko and her classmates fall through. Seiko and Naomi find themselves trapped together inside the long-demolished Heavenly Host. The two learn several things about Heavenly Host from ghosts and documents inside the building, including the school's multidimensional nature and the series of kidnappings and murders that occurred in 1973.

Seiko's death

While searching for a way out of the school, Seiko discovers to her dismay that she had lost her paper scrap of the Sachiko Ever After charm. She brings Naomi to the school's infirmary to mend her ankle (which she had sprained earlier), and then hears Yuka Mochida's voice crying out for Satoshi. Seiko briefly leaves Naomi to find Yuka, but fails and returns to Naomi to find that she has been attacked by a ghost in the infirmary. Seiko tries to comfort Naomi, but Naomi cracks under the stress she had accumulated in the school and had an argument with Seiko. Naomi accuses Seiko of not taking their predicament seriously, but Seiko argues that she's just worried about her family at home. Their spat ends with the two going their separate ways.

Seiko cries after her argument with Naomi. Continuing forward, Seiko hears a voice that is calling out for her and proceeds to follow the voice and murmurs to herself how it was the first time that she and Naomi fought. Meanwhile, Naomi has been wandering the school aimlessly with no recollection of what happened after Seiko and her split up. She regains her senses and proceeds to the third floor. Naomi hears sounds coming from the girls' lavatory and decides to investigate, finding Seiko hanged and barely alive inside one of the stalls. Despite Naomi's efforts to save her, Seiko suffocates to death.

If Seiko chooses to not follow the voice, there are several optional events that can be triggered. Examining the paper on the wall will remind Seiko of her mother who left when she was young. Seiko also can come back to the place where she and Naomi has an argument earlier. However, an earthquake will occur, and the floor that leads to where Naomi went will collapse. Going back to the the direction she came from, she wonders if she should confess her feelings to Naomi before anything bad happens to one of them, but she dismisses the thought because she feels she does not have a chance against Satoshi. She then hears the voice that's calling out for her again. Having no other direction to go, Seiko follows the voice. The rest of the event proceeds similarly to what happened if Seiko chooses to follow the voice in the first place.

CHAPTER 4

Seiko's voice warns Satoshi to take care of Naomi because she is close to snapping. Satoshi rescued Naomi, who almost killed herself by hanging, and when he questioned her why she hanged herself, Naomi didn't have any recollection of it. Satoshi assures Naomi that the same thing must have also happened with Seiko and not because of their fight with each other like Naomi had believed because he believed Seiko would not kill herself no matter how upset she was, convincing Naomi even though she still has a little doubt. They then apologize to Seiko as they can't bring her corpse along with them and continue their way.

If Naomi chooses to kiss her, Seiko will cry as she feels not ready to face her fate and wants to always be by Naomi's side. Naomi cries along with Seiko, and she eventually wakes up from her dream. If Naomi chooses not to kiss her, she will wake up from the dream immediately.

Exclusive content details end here.

CHAPTER 5

Seiko's corpse is carried by Yoshikazu Yanagihori, who cuts her tongue and drags Seiko's corpse away. Naomi then follows them, separating her from Satoshi.

"No hard feelings"

Naomi reveals to Satoshi after they and the other survivors have returned to their world that Seiko didn't commit suicide because of the influence of darkening as they had believed. After Naomi and Seiko had their heated arguments and went separate ways, Naomi, unaware of her actions under the influence of the darkening, hanged Seiko inside one of the stalls in the girls' lavatory despite the latter pleading out to Naomi to snap out of her trance. Watching the event play out from a tape recorded by Shougo Taguchi, Naomi began to succumb to the darkening as she was filled with remorse and grief over Seiko's death. Before she was completely overwhelmed by the darkening, Seiko's unsent text message miraculously arrives in Naomi's cell inbox. Naomi opened it to see the text message and initially dismissed it. The same message, with a cheerful musical riff, keeps arriving every time Naomi has guilt-ridden thoughts for Seiko, apologizing for what she has done as if Seiko was responding positively and with reassurance at every point. With Seiko's efforts, the darkening left Naomi as she continued to say "Sorry" and "I love you" to Seiko, who repeatedly responded with the "No hard feelings" text. Naomi then joined the others to perform the Sachiko Ever After correctly and return home.

EXCHAP 6

Seiko with Naomi comes to visit Ayumi, who is tending a red bean soup shop during their school's Cultural Festival. After hearing that their class got a lot of customers, Seiko mentions that it must be because of the poster that Ayumi made. Ayumi thanks Seiko for the compliment before Satoshi and Yoshiki Kishinuma come to them, asking whether they would like to join them going to a haunted house that the other class is running. Seiko and Naomi then join Satoshi and Yoshiki going to the haunted house.

Corpse Party: Book of Shadows

Prologue

The prologue continues after the True End of Corpse Party. Seiko's photo on Naomi's cellphone is seen with her face blackened out, indicating her existence has been erased.

Episode #1; 『Seal』

Seiko's head severed by piano wire

This chapter is set in an alternate timeline, continuing the event of Wrong End 6 ★8 of Corpse Party. The day loops back to the beginning of the day before everyone performed the Sachiko Ever After charm.
Seiko visits Naomi's house for their very first sleepover. She finds Naomi in her room and exclaims how the house smells like her. Naomi has a sense of déjà vu, but Seiko brushes it off. Seiko calls Yuu and tells him how she won't be coming home. They drink some chocolate soda and eat some snacks and go downstairs to eat dinner with Naomi's mother. Seiko is ecstatic over learning that Naomi talks about her a lot, and makes plans with Natsumi to go on a "date" and share facts about Naomi. Seiko and Naomi then take a bath together. Naomi washes Seiko's back and gets concerned over the faint scars over her neck, which Seiko also brushes off. Seiko tackles Naomi after she decides she needs to touch Naomi's rear end. They then get dressed and go to sleep.

Seiko mentions how happy she is and jokingly asks Naomi for a kiss, saying then she'd die a happy woman. Naomi tells her not to die at all, refusing to kiss her. Seiko asks Naomi to promise that they'd be together forever, no matter what. Naomi agrees, and Seiko goes to sleep. Naomi sleepily mentions how warm it is and Seiko wakes up, telling Naomi how she can hear her voice even in the deepest sleep, even during class. Naomi briefly scolds her for sleeping during class, and Seiko falls asleep again. Naomi cuddles the sleeping Seiko until she falls asleep as well.
Naomi and Seiko wake up and go to school. Seiko is honored to receive an umbrella from Natsumi and calls her "Mother," but is then scolded by Naomi for it. They go to school and begin preparing for the festival. Seiko then begins to touch Naomi, taking advantage of the fact that Naomi's hands are occupied with silverware. Naomi drops them.

Seiko performs the Sachiko Ever After friendship charm with her classmates. She's grouped with Naomi again. Naomi has frequent cases of déjà vu. Seiko appears when Naomi throws up after being attacked by Yoshie and is yelled at by a half-Darkened Naomi once more. Naomi begins coughing due to hair suddenly being lodged in her throat when she tries to apologize, and Seiko leaves.

Seiko wanders around Heavenly Host, crying and berating herself for allowing Naomi to get hurt and Naomi for saying such awful things. She encounters Naomi, and they embrace. They forgive each other for the events and head off to find a way out.
Seiko and Naomi pause for a break and sit in the custodian's closet. Seiko asks how Naomi's leg is and mentions her paper scrap is still missing. Seiko suddenly gets embarrassed but refuses to tell Naomi why, but she finally gives in after Naomi bugs her about it. Seiko asks for a kiss, much to Naomi's shock. Seiko says that she loves Naomi and that she wants to marry, hug, and kiss her. Naomi flees, leaving Seiko alone.

Naomi succumbs to the Darkening and begins to dream where she's in her house. She finds Seiko with a broken neck. "Seiko" calmly tells Naomi that her death is her fault and how awful she felt about it. Naomi wakes up, and "Seiko" disappears.

Naomi awakens from the Darkening earlier than she did before and managed to get Seiko down from the noose. Seiko, however, is terrified that Naomi is still possessed and flees. She runs down the stairs and gets beheaded by a piano wire. Sachiko drinks her blood while Naomi holds Seiko's severed head and cries.

Corpse Party: Blood Drive

CHAPTER 09 『 Imperator 』

As Ayumi Shinozaki and Aiko Niwa enter the main building, they hear what sounds like Seiko speaking to Naomi. Ayumi calls out her name, but to no reply. However, they hear the sound of someone running down the hallway into a classroom. Aiko and Ayumi head down the hall to the classroom, where there lies an Ouija board. Once inside, Ayumi asks if Seiko is there and if she has anything to say. The Ouija board moves, spelling out "HOW IS NAOMI?". Ayumi asks if she knows what's happening, and Seiko spells out that she cannot see from where she is. Ayumi tries to comfort her, saying how she is always on Naomi's mind. Seiko states that she is glad, and then tells her to tell Naomi that she is happy and will move on. Ayumi asks how this is true since Seiko is unable to move on. She says that it is a lie, but asks Ayumi to tell it to Naomi anyway. And the living need to move on more than she does.

CHAPTER 10 『 Reparations 』

At the end of the game, Seiko's existence is restored, along with all the others who died in Heavenly Host.

Significant plot details end here.

Relationships

Naomi Nakashima

Seiko is a very close friend with Naomi Nakashima, whom she views as a kindred spirit of sorts since they had both lost one of their parents at some point in their lives. The two live next to each other and walk to school every day together, and like to talk about their futures together. As part of her more childish, out-of-control personality, she occasionally likes to fondle with Naomi's breasts and comments on Naomi's butt as flirting, but Naomi is able to put up with it. Her feelings for Naomi are heavily implied to extend beyond mere platonic love to the point of romantic attraction, but she keeps these feelings a secret from Naomi, understanding and even supporting her feelings for Satoshi Mochida.

Satoshi Mochida

Throughout the series, Satoshi and Seiko are shown to be on good terms, being like all the others to put up with her antics. It's common that whenever he and Naomi are together, Seiko is normally not too far away, either to tease them or to observe their relationship grow. Often, Seiko tries to always bring Satoshi up in order to get Naomi to confess her feelings towards him. Satoshi is also the one to suspect Seiko didn't kill herself as he believed it wasn't like her to do so. Seiko afterward trusts Satoshi to take care of Naomi for her for the future.

Trivia

In the Corpse Party: Book of Shadows Character Contest, Seiko ranked 2nd place.

Seiko is the only one, out of all her classmates, that calls Ayumi by her first name.